Weird chainring problem.
 

Hi all!

I've been lurking here for a while, but I can't find any information on this problem that I'm having with the outside chainring on an old (late 80's) Trek 1200 that I picked up after my other bike was stolen.

Basically, the larger chainring is deformed in a really strange way. It's not the usual side-to-side lateral bend that ends up dropping the chain and wearing derailleurs. It's off-center on the axle without being bent at all. The small chainring is fine, but the large one's edge moves about a half a centimeter inward towards the axle on one side (and these are definitely not elliptical chainrings). I don't know how it happened.

Does anyone know if there are any significant problems that can be caused by this or ways to fix such a bend/dent? It doesn't look like the chainring is snagging the deraileur or anything, and I don't think I really felt it when riding. Maybe I should just let it go and stop looking for perfection on a used late 80's bike? :twitchy:

this sounds odd do you have pics? if the chainring is out of round somehow the only fix is to replace it.

Are you sure they aren't Bio Pace? That is the era when they were big on MTBs.

If they are not biopace, and you have checked that the ring is centered on the crank then it is bent and needs replaced.
Unless you don't care, which obviously you do or you wouldn't have posted.
Nothing weird about it.

Enjoy

BioPace is out of round by a lot more than 1/2 cm (1/5 in).

If the plane of the ring lies perpendicular to the axis of the axle, then you have no problem - other than an aesthetic one. The chain engages about half the ring so minor out-of-round deviations are inconsequential.

Bah, I guess they are BioPace after all! I didn't notice the engraving on the edge of the chainring until I wiped it down a bit-it's a little grubby. Haha leave it to a newbie to freak out over something like this. Thanks guys!

My first reaction to a Biopace chainring was along the lines of "good God, what hit this bike to cause the chainring to deform like that?":D
But now that I've ridden them for years I like 'em.
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